diff --git a/src/Symfony/Component/Lock/Key.php b/src/Symfony/Component/Lock/Key.php
index 743440706b669..937836951129b 100644
--- a/src/Symfony/Component/Lock/Key.php
+++ b/src/Symfony/Component/Lock/Key.php
@@ -18,7 +18,7 @@
  *
  * @author Jérémy Derussé <jeremy@derusse.com>
  */
-final class Key
+final class Key implements \Stringable
 {
     private ?float $expiringTime = null;
     private array $state = [];
@@ -91,9 +91,9 @@ public function isExpired(): bool
 
     public function __unserialize(array $data): void
     {
-        $this->resource = $data['resource'];
-        $this->expiringTime = $data['expiringTime'];
-        $this->state = $data['state'];
+        $this->resource = $data['resource'] ?? $data["\0".self::class."\0resource"];
+        $this->expiringTime = $data['expiringTime'] ?? $data["\0".self::class."\0expiringTime"] ?? null;
+        $this->state = $data['state'] ?? $data["\0".self::class."\0state"] ?? [];
     }
 
     public function __serialize(): array
diff --git a/src/Symfony/Component/Lock/Tests/KeyTest.php b/src/Symfony/Component/Lock/Tests/KeyTest.php
index 77815b25d40ae..b34f777d6020c 100644
--- a/src/Symfony/Component/Lock/Tests/KeyTest.php
+++ b/src/Symfony/Component/Lock/Tests/KeyTest.php
@@ -31,6 +31,17 @@ public function testSerialize()
         $this->assertEqualsWithDelta($key->getRemainingLifetime(), $copy->getRemainingLifetime(), 0.001);
     }
 
+    public function testLegacyPayloadCanBeUnserialized()
+    {
+        $serialized = base64_decode('TzoyNjoiU3ltZm9ueVxDb21wb25lbnRcTG9ja1xLZXkiOjM6e3M6MzY6IgBTeW1mb255XENvbXBvbmVudFxMb2NrXEtleQByZXNvdXJjZSI7czo2OiJsZWdhY3kiO3M6NDA6IgBTeW1mb255XENvbXBvbmVudFxMb2NrXEtleQBleHBpcmluZ1RpbWUiO047czozMzoiAFN5bWZvbnlcQ29tcG9uZW50XExvY2tcS2V5AHN0YXRlIjthOjA6e319', true);
+
+        $key = unserialize($serialized, ['allowed_classes' => [Key::class]]);
+
+        $this->assertInstanceOf(Key::class, $key);
+        $this->assertSame('legacy', (string) $key);
+        $this->assertNull($key->getRemainingLifetime());
+    }
+
     public function testUnserialize()
     {
         $key = new Key(__METHOD__);